Oxidation
mediated by concomitant electro-Fenton (EF) processes
in iron-based electrocoagulation (iron-EC) systems plays a crucial
role in degrading recalcitrant organic pollutants but is poorly noticed
in complex water systems. This study investigated the impact of Ca2+ on the performance of an iron-EC system based on degradation
of sulfanilamide (SA). The concomitant EF reactions in the iron-EC
system occurred under pH-neutral conditions in the presence of humic
acids (HAs) complexing with the Fe2+/Fe3+ couple.
Our results showed a significantly improved performance of EF processes
in the presence of 4 mM Ca2+ compared with that in its
absence, indicated by the SA degradation rate of up to 64%, accompanied
by 50% higher Fe2+ and a 4.7 times higher ratio of Fe2+/Fe3+. A suitable Ca2+ concentration
facilitated the cycle of Fe(II)/Fe(III) via inducing changes in solution
pH and accelerating electron transfer from HAs to Fe(II)/Fe(III)-complex
based on formation of a tribasic complex of Ca(II)/Fe(II)/Fe(III)-HAs,
as evidenced by X-ray photoelectron spectroscopy (XPS) results. This
study not only offers new insight into the role of Ca2+ in the EC process but also suggests an eco-friendly strategy to
make water treatment more sustainable.
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